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Abstract:

A nozzle arrangement includes a nozzle chamber having a roof defining an
ink ejection port and a floor defining an ink supply inlet; a magnetic
coil arrangement positioned around the ink supply inlet of the nozzle
chamber; bridge members spanning over the magnetic coil arrangement, the
bridge members supported on support posts protruding from the magnetic
coil arrangement and having a resilient characteristic; and a paddle
containing magnetic material and supported from the bridge members over
the ink supply inlet, the paddle having a shape matching that of the ink
supply inlet. The bridge members normally support the paddle in an open
position spaced from the ink supply inlet. The magnetic coil arrangement
is configured to attract the magnetic material of the paddle with a force
exceeding the supporting tension of the resilient bridge members.

Claims:

1. A nozzle arrangement comprising: a nozzle chamber having a roof
defining an ink ejection port and a floor defining an ink supply inlet; a
magnetic coil arrangement positioned around the ink supply inlet of the
nozzle chamber; bridge members spanning over the magnetic coil
arrangement, the bridge members supported on support posts protruding
from the magnetic coil arrangement and having a resilient characteristic;
and a paddle containing magnetic material and supported from the bridge
members over the ink supply inlet, the paddle having a shape matching
that of the ink supply inlet, wherein the bridge members normally support
the paddle in an open position spaced from the ink supply inlet, and the
magnetic coil arrangement is configured to attract the magnetic material
of the paddle with a force exceeding the supporting tension of the
resilient bridge members.

2. The nozzle arrangement of claim, 1, further comprising a drive
circuitry layer for providing the electrical signals to the magnetic coil
to actuate the magnetic paddle.

3. The printhead of claim 1, wherein in the open position, the paddle
permits ingress of ink into the nozzle chamber and in the closed
position, the paddle is received in the inlet to close the inlet.

Description:

RELATED AND CROSS REFERENCED PATENT APPLICATIONS

[0001] This application is a Continuation of U.S. application Ser. No.
13/037,145 filed Feb. 28, 2011, which is a Continuation of U.S.
application Ser. No. 12/272,743 filed Nov. 17, 2008, now U.S. Pat. No.
7,922,293, which is a Continuation application of U.S. Ser. No.
12/050,938 filed on Mar. 18, 2008, now issued U.S. Pat. No. 7,465,030,
which is a Continuation application of U.S. Ser. No. 11/754,367 filed on
May 29, 2007, now U.S. Pat. No. 7,364,271, which is a Continuation
application of U.S. Ser. No. 10/982,763 filed Nov. 8, 2004, now U.S. Pat.
No. 7,240,992 which is a Continuation application of U.S. Ser. No.
09/864,379 filed May 25, 2001, now U.S. Pat. No. 6,814,429, which is a
Continuation-In-Part of U.S. application Ser. No. 09/112,767, filed Jul.
10, 1998, now U.S. Pat. No. 6,416,167 all of which is herein incorporated
by reference.

[0003] This invention relates to an ink jet printhead incorporating a back
flow prevention mechanism.

BACKGROUND

[0004] The Applicant has invented a printhead chip which is capable of
printing text and images at a resolution of up to 1600 dpi. While
developing this technology, the Applicant has filed many patent
applications covering various inventions which have been conceived during
this development.

[0005] A large proportion of the inventions are in the field of micro
electro-mechanical systems. These systems allow up to 84000 nozzle
arrangements to be formed on a single printhead chip. As a result of
various constraints arising from a necessity for the high density of
nozzle arrangements, it has been necessary to design the systems in such
a way that each nozzle arrangement, in most cases, includes one or more
moving parts which serve to eject ink from each of the nozzle chambers
defined by the nozzle arrangements.

[0006] In most cases, these moving parts or components act on the ink
within a nozzle chamber to eject that ink from the nozzle chamber. The
Applicant has identified a particular difficulty to be overcome in the
manufacture of such printheads. This has to do with the back flow of ink
which is highly undesirable. The back flow of ink usually occurs after an
ink drop has been ejected from a particular nozzle arrangement where a
resulting break off of the drop and "suck back" of the ink into the
nozzle chamber causes this back flow. Further, this back flow can also
arise as a result of the operation of ink ejection mechanisms of such
printheads. Many of the ink ejection mechanisms that the applicant has
developed incorporate a reciprocal movement of one or more components.
This reciprocal movement of the components can result in a back flow of
ink as the components return to a start condition once a drop has been
ejected.

[0007] It will be appreciated that since the ink is physically ejected
from each nozzle arrangement by the movement of the nozzle components it
is extremely important that a consistent and correct amount of ink be
supplied to each of the nozzle chambers. The back flow which can result
in the absence of any mechanism to prevent it can disturb the fine
balance required to achieve the accurate supply of ink to the various
nozzle arrangements.

[0008] Attempts have been made to address the problem of back flow in
other forms of printheads such as thermal ink jet printheads. An example
of such an attempt is indicated in FIG. 1 of the drawings. Here,
reference numeral 1 generally indicates part of a thermal ink jet
printhead incorporating a back flow prevention mechanism. This printhead
1 includes an actuator in the form of a heater 2 which is positioned in a
substrate 3 defining a floor 4 of a nozzle chamber 5. An ink ejection
port 6 is positioned above the heater 2. The heater 2 heats ink 7 to an
extent which is such that the ink 7 is ejected from the ejection port 6.
It will readily be appreciated that back flow of the ink in this case
would inhibit the ejection of the ink 7 due to the loss of the required
ejection pressure. Thus, a passive flap 8 is positioned in the chamber 5.
The flap 8 is configured to bend towards a roof 9 of the nozzle chamber 5
when acted upon by the ink 7, thereby obstructing a possible back flow of
ink.

[0009] This form of back flow prevention device is not suitable for an ink
jet printhead of the type described in this specification. The primary
reason for this is that the operation of the device is dependent upon the
heating of the ink. This form of printhead does not utilize the heating
of ink to operate. Further, Applicant has found that it is highly
advantageous to incorporate a back flow prevention device in an actuator
mechanism so that a number of moving components can be kept to a minimum.

[0010] The Applicant has conceived the present invention to at least
reduce the level of back flow occurring once ink has been ejected from
the nozzle chamber, while maintaining a suitably low level of energy
consumption.

SUMMARY

[0011] According to an aspect of the present disclosure, a nozzle
arrangement comprises a nozzle chamber having a roof defining an ink
ejection port and a floor defining an ink supply inlet; a magnetic coil
arrangement positioned around the ink supply inlet of the nozzle chamber;
bridge members spanning over the magnetic coil arrangement, the bridge
members supported on support posts protruding from the magnetic coil
arrangement and having a resilient characteristic; and a paddle
containing magnetic material and supported from the bridge members over
the ink supply inlet, the paddle having a shape matching that of the ink
supply inlet. The bridge members normally support the paddle in an open
position spaced from the ink supply inlet. The magnetic coil arrangement
is configured to attract the magnetic material of the paddle with a force
exceeding the supporting tension of the resilient bridge members.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings:

[0013] FIG. 1 shows a schematic view of a prior art apparatus that
incorporates a back flow prevention mechanism;

[0014] FIG. 2 shows a schematic side sectioned view of part of a first
embodiment of an ink jet printhead, in accordance with the invention,
showing a nozzle arrangement of the printhead;

[0015] FIG. 3 shows a schematic side view of the printhead with a nozzle
arrangement in a quiescent condition;

[0016] FIG. 4 shows the nozzle arrangement of FIG. 1 in the process of
ejecting a drop of ink from a nozzle chamber of the nozzle arrangement;

[0017] FIG. 5 shows the nozzle arrangement of FIG. 1 immediately after the
ink drop has been ejected;

[0018] FIG. 6 shows a schematic side view of part of a second embodiment
of a printhead, in accordance with the invention, showing a nozzle
arrangement of the printhead;

[0019] FIG. 7 shows a schematic, side sectioned view of part of a third
embodiment of a printhead, in accordance with the invention, indicating
cross sectional detail of a nozzle arrangement of that printhead;

[0020] FIG. 8 shows a schematic, side sectioned view of part of a fourth
embodiment of a printhead, in accordance with the invention;

[0021] FIG. 9 shows a schematic, side sectioned view of part of a fifth
embodiment of a printhead, in accordance with the invention, indicating
cross sectional detail of a nozzle arrangement of that printhead;

[0023] FIG. 11 shows a schematic, exploded view of part of a sixth
embodiment of a printhead, in accordance with the invention, indicating
cross sectional detail of a nozzle arrangement of that printhead;

[0024] FIG. 12 shows a schematic view of a nozzle arrangement of the
printhead of FIG. 11 in an operative condition;

[0025] FIG. 13 shows a schematic, cross sectioned view of part of a
seventh embodiment of a printhead, in accordance with the invention;

[0026] FIG. 14 shows a schematic, cross sectioned view of part of an
eighth embodiment of a printhead, in accordance with the invention, in a
quiescent condition;

[0027] FIG. 15 shows a schematic, cross sectioned view of the printhead of
FIG. 14, in an active condition; and

[0029] The printhead shown in FIG. 1 has already been described under the
heading "Background to the Invention" above.

[0030] In FIGS. 2 to 5, reference numeral 10 generally indicates part of a
first embodiment of a printhead, in accordance with the invention,
incorporating a plurality of nozzle arrangements 12.

[0031] The printhead 10 is manufactured using an integrated circuit
fabrication technique. In particular, the printhead 10 is manufactured to
define a micro electro-mechanical system. Details of the manufacturing
process are set out in the cross-referenced applications and are
therefore not described in any detail in this specification. Further, it
is to be appreciated that, although the following description is directed
to one or two nozzle arrangements 12, the printhead 10 can incorporate up
to 19 000 of the nozzle arrangements. This has been done for purposes of
clarity and ease of description.

[0032] The printhead 10 includes a wafer substrate 14. A drive circuitry
layer 16 is positioned on the wafer substrate 14 and incorporates drive
circuitry for connection to the nozzle arrangements 12.

[0033] Each nozzle arrangement 12 includes two pairs of opposed side walls
18 and a roof wall 20 to define a nozzle chamber 22. Each roof wall 20
has an ink ejection port 24 defined therein.

[0034] An actuator 26 is positioned in each nozzle chamber 22. Each
actuator 26 includes an ink displacement member or paddle 28 which is
displaceable, in the direction of an arrow 30, towards the ink ejection
port 24 to eject ink from the ink ejection port 24.

[0035] A passivation layer 32 is positioned on the drive circuitry layer
16.

[0036] A plurality of ink inlet channels 34 are defined through the wafer
substrate 14, the drive circuitry layer 16 and the passivation layer 32
so that an ink inlet channel 34 is in fluid communication with each
nozzle chamber 22, via an inlet 35.

[0037] Operation of the actuator 26 is schematically illustrated in FIGS.
3 to 5.

[0038] A quiescent stage of the actuator 26 is shown in FIG. 3. In this
stage, the ink inlet channels 34 and the nozzle chambers 22 are filled
with ink 36 which also defines a meniscus 38 at the ink ejection port 24.
Upon actuation, the paddle 28 is driven towards the ink ejection port 24
as shown in FIG. 3. This results in the formation of a drop 40. At this
stage, the drop 40 is in fluid communication with the ink 36 within the
nozzle chamber 28 and the ink inlet channel 34.

[0039] Eventually, as a result of the momentum of the ink 36, the drop 40
is necked and separates from the ink 36 within the nozzle chamber 22 and
ink inlet channel 34. As can be seen in FIG. 5, a portion 41 of the ink
that was ejected from the chamber 22 is drawn back into the chamber 22 as
a result of surface tension effects. This has the tendency to set up a
back flow of ink in the direction of an arrow 42, which is highly
undesirable, as set out above. As can clearly be seen from the drawings,
the paddle 28 remains in a region between the ink inlet 35 and the ink
ejection port 24, thereby obstructing the back flow.

[0040] As can be seen in FIG. 3, the paddle 28 is dimensioned to
correspond generally with a cross sectional dimension of the nozzle
chamber 22. In particular, each paddle 28 is dimensioned so that, when
the paddle 28 is at rest, the paddle 28 covers the ink inlet 35.

[0041] As a result of the fact that the paddle 28 covers the inlet 35 when
at rest, the back flow of ink into the ink inlet channel 34 is inhibited
by the paddle 28. This results in the ink 36 within each of the ink inlet
channels 34 remaining relatively quiescent subsequent to drop ejection.

[0042] Furthermore, this allows the nozzle chamber 22 to re-fill in a
stable manner.

[0043] The actuator 26 includes an actuating mechanism 46 in the form of a
heater element 48 embedded in a material having a coefficient of thermal
expansion which is such that work can be performed as a result of
expansion of the material. In this particular example, the material is of
a polytetrafluoroethylene (PTFE). The heating element 48 is connected to
drive circuitry within the drive circuitry layer 16 so that operation of
the actuator 26 can be controlled with a suitable control system via the
drive circuitry within the drive circuitry layer 16.

[0044] Details of the operation and structure of the actuator 26 are
clearly set out in the above cross-referenced applications. Accordingly,
these will not be described in any detail in this specification.

[0045] In FIG. 6, reference numeral 50 generally indicates part of a
second embodiment of a printhead, also in accordance with the invention,
which incorporates a plurality of nozzle arrangements 52, one of which is
shown in FIG. 6. With reference to FIGS. 1 to 4, like reference numerals
refer to like parts, unless otherwise specified.

[0046] In the printhead 50, each nozzle chamber 22 is formed in what is
primarily an etching process in the wafer substrate 14. A silicon nitride
layer 54 is formed on the wafer substrate 14 to define the roof wall 20.

[0047] Details of the manufacture of the printhead 50 are clearly set out
in the cross-referenced applications. It follows that these details will
not be described in any detail in this specification.

[0048] Instead of being thermally actuated, the actuator 26 includes a
magnetic field generator in the form of a coil 56 which is formed on the
drive circuitry layer 16. The paddle 28 is of a material which is
responsive to a magnetic field and which is displaceable on the
application of a magnetic field of sufficient strength.

[0049] The printhead 50 does not incorporate the separate ink inlet
channels 34 extending through the wafer substrate 14. However, each
nozzle arrangement 52 includes an ink inlet opening 58 from which ink in
a reservoir, indicated at 60, can pass into the nozzle chamber 22.

[0050] It will readily be appreciated that the positioning of the paddle
28, in this particular example, inhibits the back flow of ink through the
opening 58 once an ink drop has been ejected from the nozzle arrangement
52, in the manner described earlier.

[0051] In FIG. 7, reference numeral 70 generally indicates part of a third
embodiment of a printhead, also in accordance with the invention,
incorporating a plurality of nozzle arrangements, one of which is shown
at 72. With reference to FIGS. 2 to 6, like reference numerals refer to
like parts, unless otherwise specified.

[0052] The nozzle arrangement 72, for the purposes of this invention, is
substantially the same as the nozzle arrangement 12. The nozzle
arrangement 72 has a different overall configuration to the nozzle
arrangement 12. However, the principle of operation is, again for the
purposes of this invention, substantially the same. In particular, as can
be seen in FIG. 7, the paddle 28 is restrained to move in a path that
remains between the ink ejection port 24 and the inlet 35. This is
achieved primarily by having each ink inlet channel 34 and each
respective ink ejection port 24 positioned on a common generally linear
path with the paddle 28 in that path.

[0053] Further, a side wall 74 of each nozzle arrangement 72 defines a
guide formation 76. The actuator 26 includes an actuator arm 78 mounted
on a thermal actuator 80 to drive the actuator arm 78 towards and away
from the substrate 14. The actuator arm 78 has a complementary guide
formation 82 which engages the guide formation 76. The formations 76, 82
are shaped so that movement of the paddle 28 is constrained to a
generally linear path between the ink inlet 35 and the ink ejection port
24.

[0054] In FIG. 8, reference numeral 90 generally indicates part of a
fourth embodiment of a printhead, in accordance with the invention. With
reference to FIGS. 2 to 7, like reference numerals refer to like parts,
unless otherwise specified.

[0055] In FIGS. 9 and 10, reference numeral 100 generally indicates part
of a fifth embodiment of a printhead, in accordance with the invention.
With reference to FIGS. 2 to 8, like reference numerals refer to like
parts, unless otherwise specified.

[0056] The printhead 100 includes a plurality of nozzle arrangements, one
of which is indicated at 102. The nozzle chamber 22 of each nozzle
arrangement 102 is defined in the wafer substrate 14. In particular, each
nozzle chamber 22 is formed in an etching process carried out on the
wafer substrate 14. A passivation layer 104 is formed on the substrate
14, to define the roof wall 20 and the ink ejection port 24 of each
nozzle chamber 22.

[0057] The printhead 100 does not incorporate a plurality of inlet
channels. Rather, the inlet 35 is in fluid communication with an ink
reservoir 108.

[0058] In this example, the actuator 26 includes a magnetic field
generator in the form of an electrical coil 106 positioned about the
inlet 35 of the nozzle chamber 22. The electrical coil 106 is coated with
a passivation layer 110. The electrical coil 106 is connected to the
drive circuitry of the drive circuitry layer 16 so that, when required,
the coil 106 can be activated to generate a magnetic field.

[0059] The paddle 28 is dimensioned so that, when the paddle 28 is
received in the inlet 35, the paddle 28 serves to close the inlet 35. The
paddle 28 is movable between an open position in which the paddle 28 is
spaced from the inlet 35 to permit the ingress of ink into the nozzle
chamber 22 and a closed position in which the paddle 28 is received in
the inlet 35 to close the inlet 35.

[0060] The paddle 28 is of a magnetic material 112 and is also coated with
a passivation layer 114. Thus, the paddle 28 can be displaced when the
coil 106 is activated. It follows that, by energizing the coil 106 to a
certain degree, the paddle 28 can be urged into the closed position while
ejecting ink from the nozzle chamber 22. It will therefore be appreciated
that back flow is inhibited in this case since the inlet 35 is closed by
the paddle 28 when the paddle 28 moves to eject ink from the ink ejection
port 24.

[0061] Each nozzle arrangement 102 includes two pairs of opposed bridge
members 116 which are mounted in a position spaced from the passivation
layer 110 via two pairs of opposed support posts 118. Each paddle member
28 is connected to the bridge members 116. The bridge members 116 are
configured so that each paddle member 28 is supported in the open
position. The bridge members 116 are of a resilient material so that the
paddle 28 acts against a tension in the bridge members 116 when it moves
into the closed position. The bridge members 116 therefore serve to drive
the paddle 28 back into the open position when the electrical coil 106 is
de-activated.

[0062] In FIGS. 11 and 12, reference numeral 120 generally indicates part
of a sixth embodiment of a printhead, in accordance with the invention.
With reference to FIGS. 2 to 10, like reference numerals refer to like
parts, unless otherwise specified.

[0063] In this embodiment, the actuator 26 includes an ink displacement
member in the form of a segmented disc 122. The segmented disc 122 is of
a material having a coefficient of thermal expansion which is such that
the material can expand to do work when heated to a sufficient extent.
The disc 122 has a number of segments 123 which are circumferentially
spaced. A wedge-shaped gap 124 is defined between consecutive segments
123. A central portion 126 of the disc 122 is anchored to the drive
circuitry layer 16.

[0064] In FIG. 11, the actuator 26 is in a rest position with the segments
123 generally parallel to the substrate 14. In FIG. 12, the segments 123
of the actuator 26 are bent towards the ink ejection port 24 so that a
portion of the ink 36 that is positioned between the disc 122 and the ink
ejection port 24 is ejected from the ink ejection port 24. The wedge
shaped gaps 124 accommodate this movement so that buckling of the disc
122 is avoided.

[0065] A heater element 128 is positioned in each segment 123. In
particular, each heater element 128 is positioned in a portion of each
segment 123 distal with respect to the ink ejection port 24. Resultant
uneven heating of each segment 123 causes each segment 123 to be bent
towards the ink ejection port 24.

[0066] As can be seen in FIG. 11, when the disc 122 is at rest, ink is
permitted to flow into a region 130 between the disc 122 and the ink
ejection port 24 via a space 132 defined between a periphery 134 of the
disc 122 and the roof wall 20. However, as can be seen in FIG. 12, this
space 132 is effectively closed when the segments 123 are bent towards
the ink ejection port 35, as described above. This serves to inhibit the
flow of ink through the space 132 away from the ink ejection port 35,
which, in this case, would constitute back flow.

[0067] In FIG. 13, reference numeral 140 generally indicates part of a
seventh embodiment of an ink jet printhead, in accordance with the
invention. With reference to FIGS. 2 to 12, like reference numerals refer
to like parts, unless otherwise specified.

[0068] The ink jet printhead 140 includes a plurality of nozzle
arrangements, one of which is indicated at 142, arranged on the substrate
14. The roof wall 20 of each nozzle arrangement defines a pair of ink
ejection ports 144, 146. A partition wall 148 extends from the roof wall
20 so that the nozzle chamber 22 is divided into a first part 22.1 and a
second part 22.2. The ink ejection port 144 is in fluid communication
with the first part 22.1 and the ink ejection port 146 is in fluid
communication with the second part 22.2. The ink inlet 35 is in fluid
communication with the first part 22.1.

[0069] The paddle 28 extends through one of the side walls 18 defining the
nozzle chamber 22 and into the first part 22.1. The paddle 28 is
connected to an actuator arm 150 which, in turn, is connected to a double
acting thermal actuator 152. The thermal actuator 152 is fast with a
support post 154, which provides a connection for the actuator 152 to the
drive circuitry of the drive circuitry layer 16. The actuator 152 is
configured so that, when activated, the actuator can drive the actuator
arm 150 towards or away from the substrate 14.

[0070] The paddle 28 can thus be driven towards or away from the roof wall
20. The parts 22.1 and 22.2 are in fluid communication so that, when the
paddle 28 is driven towards the roof wall 20, ink is ejected from the
ejection port 144 and when the paddle 28 is driven away from the roof
wall 20, ink is ejected from the ejection port 146.

[0071] As can be seen in FIG. 13, the paddle 28 extends over the inlet 35.
Thus, when the paddle is driven towards and away from the roof wall 20,
back flow of ink from the part 22.1 is inhibited in a manner which has
already been described.

[0072] It will be appreciated that a flow path for ink to the second part
22.2 is defined between the paddle 28 and the substrate 14. An
obstructing formation 156 is defined on the paddle 28 to extend into the
inlet channel 34. The formation 156 is dimensioned and positioned on the
paddle 28 so that, when the paddle 28 is driven away from and towards the
roof wall 20, the formation 156 remains in a position in which it
obstructs the flow of ink back into the ink channel 34. Thus, back flow
from the part 22.2 is inhibited.

[0073] In FIGS. 14 to 16, reference numeral 160 generally indicates part
of a printhead, in accordance with the invention, that incorporates a
nozzle arrangement 162. With reference to FIGS. 1 to 13, like reference
numerals refer to like parts, unless otherwise specified.

[0074] The nozzle arrangement 162 includes a nozzle chamber 164 that is
etched into the wafer substrate 14. The nozzle chamber 164 has a
substantially rectangular profile, with a pair of opposed major walls 166
and a pair of opposed minor walls 168. The ink inlet channel 34 and the
inlet 35 open into a floor 170 of the nozzle chamber 164 at a corner
between one of the minor walls 168 and the floor 170.

[0075] A passivation layer 172 of a suitable material such as silicon
nitride is positioned on the drive circuitry layer 16. In this example, a
portion 174 of the passivation layer 172 extends over the nozzle chamber
164 and defines an ink ejection port 176.

[0076] The actuator 26 includes a thermal ink displacement member 178 that
extends from the portion 174 to span the nozzle chamber 164. In
particular, the ink displacement member 178 extends to a position
adjacent one of the minor walls 168, directly above the inlet 35. The ink
displacement member 178 includes a thermal actuator 180 which is
configured to drive the ink displacement member 178 towards the inlet 35.
This serves to reduce a volume within the nozzle chamber, thereby
ejecting ink from the port 176.

[0077] An obstruction member 182 depends from the displacement member 178.
The obstruction member 182 is dimensioned so that, as the ink
displacement member 178 is driven into the nozzle chamber 164, the
obstruction member moves into a position in which ink is obstructed from
flowing into the inlet channel 34, which in this case would constitute
back flow.

[0078] Operation of the nozzle arrangement 162 is shown in FIGS. 14 and
15.

[0079] Applicant submits that by incorporating a back flow prevention
mechanism in the actuator 26, the back flow of ink, during and subsequent
to drop ejection, can be substantially prevented. As set out earlier,
this has significant advantages in the field of micro electro-mechanical
systems which are used for printing.